1. Field of the Invention
This invention relates to a chemically amplified positive resist composition which is highly sensitive to actinic radiation such as deep-UV, electron beam and X-ray, developable with aqueous base to form a pattern, and suitable for fine processing.
2. Prior Art
Resist materials are widely used in processes for the manufacture of semiconductor devices such as ICs an LSIs. To comply with the recent development toward higher integration and higher speed, further refinement of pattern rules is required. Deep-UV lithography is capable of working on the order of 0.3 or 0.4 .mu.m and makes it possible to form a resist pattern having a side wall nearly perpendicular to the substrate if a less light absorbing resist material is used.
Advanced engineers place focus on the utilization of high illuminance KrF excimer laser as a deep-UV source. A resist material having low light absorption and high sensitivity must be developed before such an excimer laser can be used in a mass scale manufacturing technique.
In this respect, recently developed chemical amplification positive resist materials using acid catalysts as disclosed in JP-B 27660/1990, JP-A 27829/1988, U.S. Pat. Nos. 4,491,628 and 5,310,619 are regarded promising as resist materials especially suited for deep-UV lithography because these materials have relatively high sensitivity, resolution and dry etching resistance and can utilize a high illuminance KrF excimer laser as a deep-UV source.
Chemically amplified positive resist materials suffer from a post-exposure delay (PED) problem and a footing phenomenon. The PED problem is that in lithographic process, line patterns would have a T-top profile, that is, patterns become thick at the top if the leave-to-stand or delay time from exposure to post-exposure baking (PEB) is extended. The footing is a phenomenon that a pattern on a silicon or titanium nitride substrate becomes widened in proximity to the substrate. It is believed that the T-top profile arises because the solubility of resist film is reduced in proximity to its surface whereas the footing arises because the solubility of resist film-is reduced in proximity to the substrate. There also occurs a problem that dark reaction of eliminating an acid labile group proceeds in a PED duration from exposure to PEB, reducing the dimension of a line to be left. These problems are serious enough to prevent chemically amplified positive resist materials from practical application.
Moreover, these problems not only complicate dimensional control in the lithographic process, but also adversely affect dimensional control in the processing of substrates using dry etching. In this regard, reference is made to W. Hinsberg et al., J. Photopolym. Sci. Technol., 6 (4), 535-546 (1993) and T. Kumada et al., J. Photopolym., Sci. Technol., 6 (4), 571-574 (1993).
It is understood that in these chemically amplified positive resist materials, air-borne basic compounds largely participate in the PED or T-top profile problem and basic compounds on the substrate surface largely participate in the footing phenomenon. Light exposure generates acid at the resist surface which is deactivated through reaction with air-borne basic compounds. As the leave-to-stand or delay time from exposure to PEB is extended, the amount of thus deactivated acid increases to retard decomposition of the acid labile group. An insolubilized layer is then formed at the resist surface, resulting in a T-top profile.
Regarding a photosensitive lithographic printing plate, JP-A 149640/1988 proposes to add an amine compound capable of capturing the acid generated upon exposure to actinic radiation, for stabilizing the sensitivity of the plate after exposure. The amine compounds used therein are 4-dimethylaminopyridine, p-phenylenediamine, and p-amino-benzoic acid. Addition of these amine compounds, however, is not effective for increasing resolution.
It is also proposed to blend nitrogenous basic compounds in chemically amplified positive resist materials to buffer the influence of contamination with basic compounds from the ambient atmosphere for thereby restraining development of an insolubilized surface layer on a resist pattern. This method, however, undesirably invites a drop of resolving power.
It is also proposed to add nitrogenous basic compounds to chemically amplified positive resist materials for capturing the acid which would otherwise diffuse into unexposed areas, thereby restraining a dimensional variation of a resist pattern. See JP-A 127369/1993, 232706/1993, 249662/1993, 249683/1993, 257283/1993, 289340/1993, 242605/1994, 266110/1994, 266111/1994, 92678/1995, 92680/1995, 92681/1995, 120929/1995, 128859/1995, 134419/1995, and 209868/1995. There is a desire to have a chemically amplified positive resist material of better quality.